Interactions of Clay Minerals with Organic Monomers

Abstract-The interactions of clay minerals with organic compounds which give rise to the formation of colored complexes, are discussed. The color reactions of clays can be ascribed to a charge transfer between the mineral and the adsorbed species. The active sites on the clay are aluminums exposed at crystal edges and/or transition metal cations in the higher valency state at planar surfaces both of which can act as electron acceptors. The pH of the system, the nature of the solvent and that of the exchangeable cation, influence the rate of color development and the final intensity and quality of the color produced. Steric factors also play a part in reactions involving bulky organics. Some practical applications based on color reactions of clays with electron-donating organic substances are described.

Section: Resultsmentioning

confidence: 95%

Mechanisms of Formation of Colored Clay-Organic Complexes. A Review

Theng¹

1971

“…The literature is replete with examples of how the crystal components of montmorillonite can participate in electron transfer reactions causing either oxidation or reduction of sorbed species under non-extreme conditions (Barshad and Kishk, 1970;Ismail, 1970;Raman and Jackson, 1966;Solomon, 1968;Theng, 1971;Theng and Walker, 1970). In addition, Meisal et al (1971) reported that Fe 3 § in mordenite can be reduced to Fe 2 § by electron transfer from perturbed water molecules on the surface or by reaction with edge AIO4 groups.…”

Section: Oxidation Reactionsmentioning

confidence: 99%

Fe²⁺-Fe³⁺ Transformations in Clay and Resin Ion-Exchange Systems

Gerstl

Banin

1980

Abstract----The pH, Eh, electrical conductivity (EC), and the amounts and valency of replaceable iron were measored periodically on Fe ~+-and Fe3+-saturated montmorillonite and cation-exchange resin at three temperatures. Differences in the pattern of change of pH, Eh, and EC with time appear to be related more to the histories and modes of preparation of the systems than to intrinsic differences in the hydrolysis of the iron in them. Electron transfer reactions involving crystal components of the clay can cause oxidation of adsorbed Fe 2 § ions; the activation energy (Ea) for oxidation on the clay's surface was 6 kcal/mole, less than a third of the activation energy reported for Fe z+ oxidation in solution. In the Fe2+-resin, where Ea = 10.7 kcal/mole, perturbed surface-water molecules may act as electron acceptors enhancing Fe 2+ oxidation.Polymerization and precipitation of the adsorbed iron is affected by the necessity to maintain electroneutrality, the ability of the iron-hydroxy ions and small polymers to move about in the voids of the ion exchanger, and the steric hindrance posed by the matrix of the ion exchanger to the formation of large polymers. In resin, little or no iron precipitates, probably due both to steric hindrance and the inability of the resin to release ionic components to maintain electroneutrality. In clays, steric hindrance is small, and AI and Mg are released from the crystal to maintain electroneutrality, thus the precipitation of iron is abundant and is controlled by the rate of release of AI and Mg from the crystal.

“…The studies of Uskov (1960 b) and of Solomon (1968), however, have made it abundantly clear that clay minerals are not chemically inert but actively influence the polymerization of organic monomers (Theng and Walker, 1970). Clays may also interact chemically with preformed polymers as evidenced by the positive difference between the integral heat of solution-wetting of a mere mechanical mixture of polymethyl methacrylatekaolinite and that of the polymer-clay composite .…”

Section: Effect Of Clay-polymer Interactions On Polymer Systemsmentioning

confidence: 99%

Interactions of Clay Minerals with Organic Polymers. Some Practical Applications

Theng

1970